Field of the Invention
The present invention relates broadly to a non-destructive system and method for detecting structural defects as well as a device and method for continuous (extended) metallic structures inspection and monitoring for possible defects; in particular, to contact and non-contact magnetic scanner device and method, using magnetic tomography for a real-time structural defects detecting; assessment of mechanical stress and categorizing the defect by the level of danger.
Background Art
This invention can be used in various fields where constructions are tested for continuity defects and other stress concentrators as well as risk-level safety factors in a contact fashion or combined with the remote method. Examples of device and method implementation may include pipes for oil and gas industry, detection of flaws in rolled products in metallurgical industry, welding quality of heavy duty equipment such as ships and reservoirs, detection of defects in bridges or cell towers, etc. It is especially important for inspection of loaded constructions, such as pressured pipes, infrastructure maintenance, nuclear power plant monitoring, bridges, corrosion prevention and environment protection.
Railroads, electric transmission lines, bridges, cell towers, and pipelines have an important role in the nation's economy. These engineering structures do occasionally fail. Failure of these key infrastructure elements can cause economic disruption as well as put lives at risk.
Major causes of metallic infrastructure failure around the world are external interference, corrosion, and fatigue cracks; therefore, assessment methods are needed to determine the severity of such defects when they are detected in infrastructure, experiencing different loads.
Structures such as bridges, power transmission wires, wind turbines, and cell towers are important components of national infrastructure that require maintenance and examination for defects in order to allow detection of flaws that would result in failure. They are also all characterized in that these structures are often difficult to access due to their height, length, and sometimes the additional local loads they carry, i.e. bending, warping, exposure to wind, currents, etc. By mounting non-destructive non-contact detection sensors to a drone one can both conduct a thorough assessment of defects in the structure, rate the defects in terms of likelihood to cause structural failure and determine the priority and necessity of repairs and do this assessment without risk to human life as a drone equipped with sensors can access these places with greater ease than people can. For example, rather than lowering a bridge inspector on a crane bucket to examine the underside of a bridge a drone could be flown beneath the bridge and perform the inspection.
There are several magnetographic devices that have been disclosed for non-destructive inspection of ferrous materials. In magneto-graphic inspection and defectoscopy the tested area of the material is placed in proximity to the magnetic medium. The changes of the surface-penetrating impede flux due to the material flows or deviations can be recorded. The resulting “magnetogram” of the material can provide the information about the location, size, and type of the defect or abnormality. In general, this information can be convened into the report about the quality of the material. Obtaining the magnetogram (magnetic picture) of the material in the course of the non-destructive inspection process is very challenging and typically requires additional forms of inspection, such as roentgenogram or an X-ray image.
For example, U.S. Pat. No. 4,806,862 (Kozlov) offers a contact method of magnetographic inspection of quality of materials, where a magnetic substance (such as liquid) is applied to be magnetized together with the tested material. According to the invention, the intensity of the magnetizing field is established by the maximum curvature of the surface of a drop of a magnetic fluid applied onto the surface of the material to be inspected, so that the resulting magnetogram can be used to assess the quality of the material.
In another magnetographic U.S. Pat. No. 4,930,026 (Kljuev), the flaw sensor for magnetographic quality inspection is disclosed, which includes a flaw detector and a mechanism for driving the magneto-sensitive transducer. During the scanning procedure, the magnetic leakage fluxes penetrate through the surface of the material in place where flaws occur, resulting in a magnetogram of the tested material.
The deviations of F-value can be classified according to a level of mechanical stress concentration—as follows: X1—for negligible detects (good technical condition of the metal); X2—for defects that require planned repairs (acceptable technical condition); X3—for defects that require immediate repairs (unacceptable, pre-alarm technical condition, alarm).
The absolute values X1-X3 of the F-value (comprehensive value of magnetic field anomaly) should be defined for each particular case, depending upon the following factors: i) Material type (e.g. steel); ii) Topological location with the local background magnetic fields variation range, iii) Distance to the object (e.g. pipe-line installation depth), iv) General condition of the deformation-related tension within construction under testing, v) etc.
As a result, the only relative changes (variations) of the magnetic field can be evaluated, for the given defective segment (relatively to the flawless segment), by comparing to its relative F-values. Thus, the very moment of the ultimate stress-limit crossing can be identified for each defective segment during the real operation (i.e. under pressure/loaded) condition. It can be done by monitoring the development of the defects within its F-value interval, namely, starting from the good technical condition X1 up until the yield-strength limit approaching and material breakdown. It provides a real possibility to predict the defect's speed development, resulting in increased accuracy in priority order definition for upcoming maintenance steps.
The aforementioned techniques are not satisfactory to be used for efficient prediction in defects development timeline and not capable of providing a real-time alert about the strength-limits approaching, i.e. when probable construction failure is about to occur.
The closest remote technology to the disclosed invention is shown in RU 2264617 that describes the Magnetic Tomography (MT) technique. This technique includes a remote magnetic field vectors measurement in Cartesian coordinates with the movement of measuring device (magnetometer) along the pipe-line, the recording of the anomalies of magnetic field (on top of background magnetic field), processing of the data and report on found pipe-line defects with their localization shown in resulting magnetogram. The technique provides a good sensitivity, also capable of discovering the following types of defects: i) Changing in geometry: dents, wavy surface, deformed shape of cross-section; ii) Metal loss, having mechanical, technological or corrosion nature; material discontinuity: layering and inclusions; iii) Cracks; iv) Welding, flaws, including girth weld defects. Moreover, such method provides a risk-factor ranking of the discovered pipe-line defects accordingly to material tension concentration (factor F). Accordingly this technique was taken as initial prototype for the disclosed technology.
MT determines the comparative degree of danger of defects by a direct quantitative assessment, of the stress deformed state of the metal. Conventional surveys only measure the geometrical parameters of a defect. Their subsequent calculations to assess the impact of the defect on the safe operation of the pipe do not take into consideration the stress caused by the defect. Therefore conventional surveys may fail to detect dangerously stressed areas of the structure or, conversely, classify a defect as one which requires urgent attention when, in reality, the stress level may be low and the defect presents no immediate threat to the operation of the structure. Since MT directly measures the stress caused by defects it is an inherently more accurate guide to the safe operation of the structure than conventional survey methods.
There are several methods for integrity assessment of extended structures (e.g. metallic pipes) that have been proposed in literature. Thus, U.S. Pat. No. 4,998,208 (Buhrow, et al) discloses the piping corrosion monitoring system that calculates the risk-level safety factor producing an inspection schedule. There is another method disclosed in U.S. Pat. No. 6,813,949 (Masaniello, et al.), which addresses a pipeline inspection system having a serviceability acceptance criteria for pipeline anomalies, specifically wrinkles, with an improved method of correlating ultrasonic test data to actual anomaly characteristics.
The main disadvantages of previous methods are: i) The scope of its application is limited by large-scale linear objects and necessity to contact the surface. Located at a considerable distance from each other, ii) Difficult real-time implementation of the device, iii) It is impossible to identify the location of individual defects, visualize and specify the exact position on the internal or external tested surfaces; iv) There is also a lack of visualization of the obtained information in a form of the resulting tomogram where all the locations of the defective segments with associated respective risk factors (absolute mechanical stress values) are shown.
There is a need in developing a combination of contact and remote techniques in order to increase sensitivity, resolution and visual representation of the stress-related anomalies within the structure, as well as a probability of operation failure (i.e. risk-factor).
The defect areas risk-factor criteria and ranking (such as material stress: F-value) is used for planning a required sequence of repair and maintenance steps. Such criteria were developed by comparing a risk-factor calculated using the defect geometry in calibration bore pits with a predicted risk-factor obtained by the remote magneto-metric data (i.e. comprehensive F-value of particular magnetic anomaly).
In the traditional method, there is no evaluation of cracks stability, that is, no prognosis for the rate of crack-like defects development, especially in a longitudinal direction. There is also no evaluation of danger of other types of defects (e.g. welds) due to operation conditions, as the evaluation of metal properties degradation in aggressive conditions and with anomalies of stress-deformed state (SDS) is not carried out. For example, there are bridge sections with sags, bends, stresses/stretches/twists, that is, with loss of a bridge or pipes stability. In addition, the main problem—the degree of stress concentration in a particular bridge section—is not considered; it must be considered by engineers of the integrity department of the company/operator by e.g. expert evaluation, and it requires additional data about all local loads.
As an alternative to the above method, a magnetometric tomography method (MTM) has been proposed. MTM is a non-contact method of non-destructive testing (NDT) and technical diagnostics based on remote scanning the magnetic field of a ferro-magnetic structure in a system of orthogonal coordinates. Additionally, manual processing and calibrating are used to define locations of sections with metal defects of various types and other stress concentrators, identify the type of the most dangerous defects, and evaluate serviceability of defective sections according to the degree of mechanical stress concentration.
However, MTM is currently available only to pipeline based application (both on-shore and under water). Also the current, detection capability of such a magnetometer is only up to a maximum distance of 20 times the structural member diameter. Thus, such conventional MTM systems are not suitable for many structures, which may be located at significant height. The inspection speed is also limited to only about 2 meters per second (m/s), and the recording of distance is typically manual. Also, the analysis of the collected data is substantially manual, i.e. it relies again on expert evaluation.
A need therefore exists to provide a system and method for inspecting a structure with height or at altitude that seeks to address at least some of the above problems.